Rheostat



(No Model O LE.

RHEOSTAT.

Patented Feb. 3, 1885.

UNITED STATES PATENT OFFICE.

JOHN DOYLE, OF HOBOKEN, NE\V JERSEY, ASSIGNOR TO HIMSELF, AND O. COLESDUSENBURY, OF \VHITE PLAINS, NE\V YORK.

R H EOSTAT.

SPECIFICATION forming part of Letters Patent No. 311,820, dated February3, 1885.

Application filed March 31, 1884.

To all whom it may concern.-

Be it known that I, JOHN DOYLE, of Hoboken, in the county of Hudson andState of New Jersey, have invented an Improvement in Rheostats, of whichthe following is a specification.

Rheostats for electric currents have been made with a sliding contact,by the movement of which more or less of the resistance has been placedin the electric circuit. The resistance has been uniform throughout; butthe variation in the resistance has resulted from the greater or lesslength of the resisting material in the circuit. It has long been knownI 5 that the conductivity of difierent substances varied, some beingvery poor conductors and others better conductors of electricity. Inelectric lamp circuits the rheostat should be small, so as not to occupymuch space, and at the same timethe range of the resistance should belarge. My present invention relates to a rheostat having resistancesthat occupy but little space, and are composed of substances having difierent degrees of conductivity, andI group these together in such amanner as to occupy but little space, and surround them with an envelopethat is anon-conductor of heat, so that any heat developed in therheostat will not 0 become a source of danger.

In the drawings, Figure l is a sectional elevation, and Fig. 2 is an endview, of the rheostat in an enlarged size. Fig. 3 is a separate view ofthe resisting sections in contact with each other, and having a movablecontact.

The heads a I) are of glass or other nonconducting material. The wires 0pass through holes in the head a, and the wires (1 pass through holes inthe head I). There is a space between the end of one wire 0 and the endof the corresponding wire d, and this space is to be more or less, asrequired. The respective wires 0 d in line with each other are united bymaterials of inferior but differ- 5 ent specific conductivity, as at 1 23 4 5 6 7 8.

Ihave used and find suitable a mixture of plumbago and boraX moistenedwith alumwater, and molded, pressed, and baked around the adjacent endsof the respective wires 0 d.

I find that the resistance is increased in proportion to the quantity ofborax made use of.

(No model.)

l Vhen there is but little borax, the plumbago offers very littleresistance. As the proportion of borax is increased so the resistance isinlamp-black, especially in rheostats requiring high resistance, thelamp-black being an equivalent of the borax,and acting in a similar manner, except that the borax ac'js to harden the plumbago.

In making my rheostat the compound is mixed with reference to theresistance required. For instance, the spaces between the ends of theconductors c (I may be half an inch. Then the composition for N0. 1 isto be the lowest resistance and for No. S the highest resistance. Thecomposition, being placed around the ends of the respective pairs ofwires, is firmly pressed and then dricdand baked.

Upon the head a, I place a rotary switch, 2', to the center of which theconductor is connected by the spring 1); and this switch i may be turnedaround into contact with the endof either pin or wire 0, so that theelectric cir cuit will be closed through the particular rheostatconnected with that wire 0. The circuit-wire f is connected with theouter ends of all the wires (1. By turning the switch in one directiongreater resistances will be brought successively into the circuit, andthe reverse. The end of the switch should be wide enough to reach fromone wire 0 to the next, so as to touch the second wire before leavingthe first wire, thus preventing a spark. The rag 0r ratchet wheel Z hasteeth that are inclined in both directions and equal in numbers to thewires 0, and a spring-pawl, mpressing against such teeth, holds theswitch at any place to which it may be moved, and completes a movement,if carelessly made, by turning the switch and holding it in contact withonly one of the wires 0. The wires 0 (I may be zigzag, or bent back uponthemselves, as shown in connection with rheostat No. 5, so as toincrease their length and lessen the heat conducted to the heads a 1).Around the rheostat-I apply acase, in, of material that is a poorconductor of heatsuch as asbestus cloth or mica-wrapped aroundtheheads ab, and secured to the same by a binding of wire or otherwise. Thisprevents external contact with either of the resistances,

, creased. I also find it advantageous to use some and avoids risk offire or injury in consequence a rheostat, of a range of materials ofdifferent of any heat developed by the electric current in passingthrough the rheostat or resistance heating such resistance. Asafurtherproteetion, 1 use a volute, p of heavy wire near eac-li'end ofthe instrument. One end ofeach is connected with one of the heads, andthe other end is connected with a covering, q, of perforated tin orother suitable material, there being, by preference, a head, 1', at theback end to inclose the circuit-connections. The covering q is held inplace by the Volutes of wire, and does not become heated at its outerends, even if the heads are hot, and the air-space between theheads andcase and the covering q p re vents any heat being conducted to orradiated from the said covering g. This instrument occupies very littlespace, and can be constructed with such a variety of poor conductorsthat the required resistance can be brought into the lamp or otherelectric circuit. In cases where the inferior conductingmaterialspossessing different specific resistance, as afo resaid, are placed sideby side or united up into a rod or single piece, as seen in Fig. 3, thecircuit-conductor f can be connected at one end, and the movable switchdevice 1 may be slid along overand in contact with such varyingresisting material to bring into action the desired resistance.

I claim as my invention- 1. The combination, with the conductors in I il r I l specific conductivity, and a movable switch device for directingthe current through the desired resistance, substantially as set forth.

2. The conductors 0 (Z and theheads ab, supporting the same, incombination with the connections of different specific conductivitybetween the respective conductors, and a movable switch, substantiallyas set forth.

8. The combination of the heads a b, conductors 0 (Z, resistances ofdifferent specific conductivity, the switch, the circuit-connections,and the surrounding case of non-c011- ducting material, substantially asset forth.

4. The heads a b, in combination with the conductors 0 (Z, theresistances of different specific conductivity uniting such conductors,the switch, the non-conductin case and surrounding covering q, andcoilsp'", substantially as set forth.

5. A rheostat having a resistance composed of plumbago and borax, or itsequivalent, mixed together. the resistance varying in proportion to thehora-X present in the mixture. substantially as set forth.

Signed by me this 26th day of March, A. D. 188k.

JOHN D OYLE.

Witnesses;

Geo. T. PINCKNEY, WILLIAM G. Mo'r'r.

